1. Field of the Invention
The present invention relates to a method and apparatus for forming a silicon oxide film by CVD on a target substrate including a metal surface, and particularly to a film formation technique used for a semiconductor process. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an LCD (Liquid Crystal Display) or FPD (Flat Panel Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In manufacturing semiconductor devices for constituting semiconductor integrated circuits, a target substrate, such as a semiconductor wafer, is subjected to various processes, such as film formation, oxidation, diffusion, reformation, annealing, and etching. In order to perform these various processes, a vertical heat processing apparatus of the batch type is known, in which a number of wafers are processed together for, e.g., a film formation process (for example, Jpn. Pat. Appln. KOKAI Publications No. 9-246257 and No. 2002-9009).
FIG. 6 is a structural view schematically showing a conventional vertical film formation apparatus (CVD apparatus). As shown in FIG. 6, the apparatus includes a vertical process container defining a process field in which target substrates or semiconductor wafers W are horizontally supported at intervals in a vertical direction. The wafers W are heated at a predetermined temperature, e.g., within a range of about 600 to 700° C., by a heater 6 disposed around the process container 2. An Si-containing gas, such as monosilane or dichlorosilane (DCS), and an oxidizing gas, such as O2 or N2O gas, are supplied from below the process field by a film formation gas supply section 8. Further, the interior of the process container 2 is vacuum-exhausted by a vacuum exhaust system 12 through an exhaust port 10 formed at the top of the process container 2. The process field is thus set at a predetermined pressure and a predetermined temperature to form a silicon oxide film on the wafers W by CVD.
There is a case where the surface of a metal material (metal surface), such as a metal electrode, metal interconnection, or metal gate electrode, is exposed on a wafer W. In this case, when an oxide film, such as a silicon oxide film, is formed on the wafer, the metal surface is oxidized and thereby deteriorated as regards electric characteristics. For this reason, conventionally, in such a case, a barrier layer, such as a silicon nitride film or metal nitride film, is first formed on the metal surface. Since the metal surface is covered with the barrier layer, the metal surface is prevented from being oxidized in forming the oxide film.
Incidentally, there is a method of intermittently supplying a film formation gas into a process container to laminate oxide films of an atomic layer level or molecular layer level. Film formation methods of this kind are called ALD (Atomic Layer Deposition) or MLD (Molecular Layer Deposition). Also in ALD and MLD, where an oxide film is formed on a wafer including a metal surface, it is necessary to first cover the metal surface with a barrier layer.
As described above, according to conventional film formation methods, where a silicon oxide film is formed on a wafer including a metal surface, a barrier layer is formed in advance. Consequently, it is necessary to add a step of forming this barrier layer and thus increase the number of manufacturing steps. Further, the barrier layer is formed of a nitride film, such as a silicon nitride film, which has a high tensile stress. This stress may deteriorate some of the electric characteristics of a semiconductor device.